In the operation of large scale combustion devices such as coal burning boilers, there is a continual build up of slag deposits on their internal walls and heat transfer surfaces. As the slag builds up on these surfaces, the slag layer reflects some of the radiant heat energy produced within the boiler by combustion and thus, less steam and thermal output is produced by the boiler. Accordingly, it is important to periodically remove the slag layers to maintain efficient operation.
Various means for detecting the presence of slag development on internal surfaces of combustion devices have been developed. One approach is through the monitoring of various operating parameters of the boiler which provide an indirect indication of the development of such slag as efficiency is adversely affected. When slag deposits reach a point where cleaning is needed, various cleaning technologies are used. For example, sootblower systems are used which project a stream of fluid cleaning medium against the surfaces, such as air, steam, or water. These fluids remove the slag through a combination of heat quenching which embrittles the coating and mechanical impact energy which causes the encrustations to lose their adherence to the surfaces and fall away. Other approaches include mechanical rodding and shakers which vibrate the surfaces to remove the layers.
For efficient boiler operation, it is desirable to clean surfaces only when needed. Operating sootblowers causes an efficiency penalty for the boiler when it is not used then at a time when it is actually needed. Operating cleaning systems based strictly on time or other indirect measures can result in operating the cleaning devices on a schedule which is not optimal.
It is known that the inside surfaces of a boiler can be imaged using cameras sensitive to infrared light. These devices employ an objective lens positioned inside the boiler which images a wall surface of the boiler. Although these systems are effective in many applications, they have the shortcomings of high cost and sophistication, as well as the requirement for complex image processing. Moreover, since the wall being imaged is typically some distance from the objective lens, disturbances such as the fireball or products of combustion in the boiler can interfere with the clear visibility of the surfaces being imaged. Such cameras generally have lens tubes of a diameter of two inches or more, which pose installation difficulties in penetrating the boiler outer wall.
Another approach toward detecting the state of cleanliness of interior boiler surfaces is through the use of so-called heat flux sensors. These devices are typically thermocouple elements mounted to the steam tubes which carry the steam being produced by the boiler. When the temperature of the internal surface of the boiler and the steam carried within the pipe adjacent to that surface approach one another, it is then known that the rate of heat transfer from the combustion processes in the boiler has been reduced. This is an indirect indication of the development of slag encrustations and can be used to activate cleaning systems.
There is a need in the art to provide additional mechanisms for the detection of slag build ups on internal surfaces of combustion systems including coal fired boilers. Ideally, the device would be relatively inexpensive to manufacture, install, and use, be durable, require little maintenance, and reliably and accurately detect the presence of slag development.